1. Field of the Invention
The present invention relates to a center-of-gravity determining circuit for pulse generation which obtains a manipulated variable required to control an actuator or the like by using results of fuzzy reasoning.
2. Description of the Prior Art
Fuzzy information obtained as a result of fuzzy reasoning appears in the form of electric signals distributed over a plurality of lines. Accordingly, it is necessary in order to control an actuator or the like by using these signals to convert them into a manipulated variable. A converting mechanism designed for this purpose is called defuzzifier. In general, the conversion is performed by arithmetically determining the center of gravity of fuzzy quantities (JP Appln No. 63-206007, 1988).
The prior art will be explained below on the basis of the contents of the above-mentioned publication.
One example of fuzzy information will be explained with reference to FIG. 6. Elements of fuzzy information are denoted by x, and it is assumed that there are discrete values x.sub.1, x.sub.2, . . . x.sub.n-1, x.sub.n. These elements are output onto a plurality of signal lines l.sub.1, l.sub.2, . . . l.sub.n, respectively, and grades (functional values corresponding to variables) .mu..sub.1, .mu..sub.2, . . . .mu..sub.n corresponding to these elements are represented by analog voltages or current signals appearing on the respective signal lines.
In this case, the grades .mu..sub.1, .mu..sub.2, . . . .mu..sub.n are assumed to be represented by voltages. In FIG. 6, the center of gravity (position on the X axis) of fuzzy information is given by ##EQU1## Accordingly, multiplication, addition and division are needed to obtain the center of gravity.
Therefore, in order to obtain the center of gravity only by addition, Equation (1) is transformed into Equation (2), and the latter is adjusted so that the denominator in Equation (2) is 1: ##EQU2##
That is, if K is adjusted so that the denominator is 1, the center of gravity can be obtained from Equation (3): ##EQU3##
Referring to FIG. 7 which is a specific circuit diagram, voltages .mu..sub.1, .mu..sub.2, . . . .mu..sub.n representative of elements of fuzzy information are led out onto n signal lines l.sub.1, l.sub.2, . . . l.sub.n and then multiplied by the coefficient K in a variable-grade reasoning engine 1. Fuzzy quantities K.mu..sub.1, K.mu..sub.2, . . . K.mu..sub.n output from the reasoning engine 1 are input to both a weighted summing circuit 2 and a simple summing circuit 3. In the weighted summing circuit 2, calculation of the right-hand side of Equation (3) is executed to output a voltage signal representative of the center of gravity.
In the meantime, the simple summing circuit 3 executes calculation of the denominator of Equation (2) and inputs the result of the calculation to a voltage adjusting circuit 4. The other input terminal of the voltage adjusting circuit 4 is supplied with a voltage corresponding to the grade 1. Accordingly, in response to the output signal from the voltage adjusting circuit 4, the coefficient K in the variable-grade reasoning engine 1 is adjusted so that the output from the simple summing circuit 3 is 1 at all times.
According to the above-described prior art, the output signal from the simple summing circuit 3 for electric signals distributed over a plurality of lines is controlled so as to be equivalent to 1. In general, this type of control is executed by using a membership function circuit that is provided with a grade control means. In this case, no dividing circuit is needed, and the circuit configuration is simplified correspondingly, resulting in an increase in the operating speed, but on the other hand, the membership function circuit becomes complicated, and a control mechanism must be added.
In a case where the manipulated variable is the width of a pulse (e.g., an injector drive control signal of a fuel injector device or an ignition timing pulse), the determined value is output in the form of a voltage, and it is therefore necessary to provide an interface for converting the output voltage into a pulse width.